In recent years, there has been a demand to reduce tire rolling resistance from the perspective of low fuel consumption at the time of vehicle traveling. In addition, there has been a demand for improvements in wet performance from the perspective of safety. A known method of achieving this is a method of establishing both low rolling resistance and wet performance by adding silica to a rubber component constituting the tread part of a tire.
However, silica has low affinity with rubber components, and the cohesiveness of silica components is high, so even if silica is simply added to the rubber component, the silica is not dispersed, and which leads to the problem that the effect of reducing the rolling resistance or the effect of improving the wet performance cannot be sufficiently achieved.
Under such circumstances, the present applicant proposed a rubber composition containing a modified polymer capable of reacting with silica (Japanese Unexamined Patent Application Publication No. JP2012-131983A) and a rubber composition containing a mercaptosilane capable of reacting with silica (Japanese Unexamined Patent Application Publication No. JP2010-270247A) as techniques for dispersing silica.
In addition, there is also a demand for there to be little crosslinking (rubber burning) in the rubber composition for a tire tread at the storage stage or the stage before the vulcanization process. That is, there is a demand for excellent processability (for example, for the composition to have an appropriate viscosity and excellent scorch resistance and extrudability; same hereafter).
In recent years, environmental issues and resource problems have led to a demand for even lower fuel consumption in vehicles, which in turn has led to a demand for further improvements in the low rolling resistance of tires. In addition, in step with improvements in the required safety level, there has also been a demand for further improvements in wet performance. Due to such reasons, the present inventors assessed that there is room for improvement in the low rolling resistance or wet performance of a conventional rubber composition containing a mercaptosilane that can react with silica.
Under such circumstances, when the present inventors researched rubber compositions containing a conventional conjugated diene rubber and the mercaptosilane used in the rubber composition described in Patent Document 2, it became clear that the low rolling resistance, wet performance, and processability do not satisfy the currently required levels. In addition, when the present inventors researched rubber compositions containing the modified polymer used in the rubber composition described in Patent Document 1 and the mercaptosilane used in the rubber composition described in Patent Document 2, it became clear that the processability does not satisfy the currently required level.